1. Field of the Invention
This invention relates generally to an optical sensor for controlling operation of the windshield wipers of an automobile in response to the presence or absence of moisture upon the external surface of the windshield of the vehicle, and more particularly to the mounting of the optical sensor upon the interior surface of the windshield.
2. Description of the Prior Art
Motor vehicles have long been equipped with motor-driven windshield wipers for clearing moisture from the external surface of the windshield, at least within the driver's field of vision, and generally over a larger area so as to enhance vision through the windshield. Early model vehicles included a manually operated on-off switch by which the vehicle driver controlled operation of the wipers. Later model vehicles were provided with a two-position switch which allowed operation of the wipers at either a slow or a fast speed to accommodate different rates of rainfall or moisture deposition on the windshield. Still later, multiposition or variable speed switches were provided which allowed the driver to select a wide, if not an infinitely variable, range of speeds to suit conditions. More recently, wiper controls have included a delay feature whereby the wipers operate intermittently at selected time delay intervals.
There has now been developed an improvement over the aforementioned manually operated windshield wiper motor control wherein the motor is automatically activated when moisture is deposited upon the surface of the windshield or other vehicle window upon which a wiper may be employed, such as the rear window. Control devices for providing such automatic activation are disclosed, for example, in U.S. Pat. Nos. 4,476,419 to Fukatsu et al; 4,355,271 to Noack; 4,131,834 to Blaszkowski; 4,463,294 to Gibson; and 4,495,452 to Boegh-Peterson. U.S. Pat. No. 4,620,141 to McCumber et al discloses an automatic control circuit for triggering a sweep of the wiper blades in response to the presence of water droplets on the exterior surface of a windshield, wherein a block-like sensor housing is mounted upon the interior surface of the windshield. The construction of the sensor and its associated circuitry are fully described in the patent, and the disclosure is incorporated herein by reference.
A number of the sensing or detecting units for automatic wiper activation operate upon the principle of a light beam being diffused or deflected from its normal path by the presence of moisture on the exterior surface of the windshield. In one such device a box-like housing may be mounted upon the interior surface of the windshield. The housing is provided with a first set of bores therethrough which are disposed at a predetermined angle to the plane of the associated area of the windshield. Light pipes or rods and light-emitting diodes are fitted within the bores. A corresponding second set of bores is disposed at an angle to the first set such that their longitudinal axes would intersect at points on the exterior surface of the windshield when the housing is affixed to the interior surface. Light conducting rods and photosensitive devices are contained within the second set of bores. Light from the light-emitting diodes is reflected back from the air-glass interface, that is, the outside surface of the windshield to the photo-detectors. The presence of moisture on the surface of the windshield affects the reflection of light at the air-glass interface, and this change in reflected light is electronically processed and utilized as the signal for activating the windshield wipers.
In order for the system to operate properly the sensor housing must remain in a fixed position relative to the windshield surface, and the light pipes or rods must be optically coupled to the windshield so as to prevent spurious reflection of light from the interior surface of the windshield as would be caused, for example, by moisture condensation or dust accumulation on the surface. In other words, the sensor housing should securely engage the windshield and be optically coupled to the windshield so as to effectively eliminate the interface between the light pipes or rods and glass surface from an optical standpoint. Various devices have been proposed for mechanically and otherwise urging the sensor housing into face-to-face engagement with the windshield surface. Such devices are often difficult to mount and aesthetically unattractive, and they tend to inordinately obstruct the driver's view. Thus, none has proven entirely satisfactory in mounting the sensor housing upon the windshield.